Shirou is a 12-year-old troublemaker who's half Japanese, half Chinese. He left his village at 10 to chase his dream of becoming a Super Chef, but after two years of traveling with nothing to show for it, he panicked and faked the credentials when he got back home. That didn't last long—a cooking official called him out on the fake badge almost immediately.
Enter Mao. When Shirou found out Mao was the real deal, he basically attached himself to the guy and hasn't let go, traveling with him and Mei Li ever since. In the manga, he first crossed paths with Mao after getting caught stealing food; in the anime, Mao and Mei Li stumbled across him passed out from hunger in the forest.
Shirou's not exactly a cooking prodigy, but he knows his way around a kitchen better than Mei Li does—though "average" is probably the fairest description of his actual skill level. What he is good at is causing chaos. He constantly harasses Mei Li by groping her, which usually ends with her smacking him around. Fans often note that despite all the trouble he stirs up for the group, there's something endearing about how earnest he is about his dream.
Eventually he lands a gig as a chef-in-training at Yang Spring Restaurant, which feels like a legitimate step toward actually making good on that Super Chef promise.
Content compiled by AnimeList.moe from publicly available sources.